2014 Articles

Twenty-first century reversal of the surface ozone seasonal cycle over the northeastern United States

Clifton, Olivia Elaine; Fiore, Arlene M.; Correa, Gustavo P.; Horowitz, Larry W.; Naik, Vaishali

Changing emissions can alter the surface O3 seasonal cycle, as detected from northeastern U.S. (NE) observations during recent decades. Under continued regional precursor emission controls (>80% decreases in NE NOx by 2100), the NE surface O3 seasonal cycle reverses (to a winter maximum) in 21st century transient chemistry-climate simulations. Over polluted regions, regional NOx largely controls the shape of surface O3 seasonal cycles. In the absence of regional NOx controls, climate warming contributes to a higher surface O3 summertime peak over the NE. A doubling of the global CH4 abundance by 2100 partially offsets summertime surface O3 decreases attained via NOx reductions and contributes to raising surface O3 during December–March when the O3 lifetime is longer. The similarity between surface O3 seasonal cycles over the NE and the Intermountain West by 2100 indicates a NE transition to a region representative of baseline surface O3 conditions.